What Is Electrode Potential?

Regardless of whether it is an electronic conductor or an ionic conductor, according to the theory of physical chemistry, where solid particles come into contact with the liquid phase, an even layer must be generated at the interface. It is a closed and even electric layer, so no external electric field is formed. The potential difference between them is called the electrode potential.

Standard electrode potential is standard hydrogen

Judging the direction of the spontaneous redox reaction

Battery reactions are spontaneous redox reactions. Therefore, the direction of the battery reaction is the direction in which the redox reaction spontaneously proceeds. When judging the direction of the redox reaction, the reaction can be divided into two half reactions, and the electrode potential can be obtained. Then according to the principle that the high potential is the positive electrode to initiate the reduction reaction, and the low potential is the negative electrode to initiate the oxidation reaction, the direction of the spontaneous reaction can be determined. If the values of the two pairs are significantly different (that is, E ), the change in concentration has little effect on the potential, so that the reaction does not change direction. Therefore, when E > 0.2V, the reaction direction can be directly determined by the value even if it is not in the standard state. Otherwise, the influence of concentration and acidity must be considered, and the value of the electrical pair is calculated using the Nernst equation. E> 0 is used as a judgment to determine the direction of the reaction. If E> 0, the forward reaction can proceed spontaneously; E <0, The forward reaction cannot proceed spontaneously, and the reverse reaction can proceed spontaneously.

Example 1 Determine the direction of the following reactions at 298K:

Cu ²⁺ (0.00001mol·L ^-1 ) + Fe Cu + Fe ²⁺ (1.0mol·L)

Solution: Write the above reaction into two

Metals can be thought of as consisting of ions and free electrons.

Metal ions are arranged in dots, and electrons move between them. For a given electrode, the electrode potential is a definite constant. For the following electrode reactions:

aA + bB <=> cC + dD + ne

The electrode potential can be expressed as

(1.1)

Where

E: electrode potential, V;

Eo: standard electrode potential, V;

R: gas constant, 8.31441J / (mol · k);

T: absolute temperature, k;

n: the number of electrons participating in the electrode reaction;

F: Faraday constant, 96486.7C / mol;

a: The activity of each substance involved in the chemical reaction.

Equation (1.1) is a basic relational expression of electrode potential.

The single electrode potential cannot be measured because when the solution is connected with a wire, a new solution-electrode interface is created and a new electrode is formed. At this time, the measured electrode potential is no longer the potential of the single electrode. , But the potential difference between the two electrodes. At the same time, the potential of the electrode under study can only be determined by measuring the electromotive force of the galvanic cell by combining the potential of the electrode to be studied with the potential of another electrode as a potential reference standard.